Touch detection for capacitive touch screen

ABSTRACT

A touch-screen device includes a transparent dielectric layer. A plurality of first electrodes is located over the transparent dielectric layer. A plurality of second electrodes is located under the transparent dielectric layer so that the first electrodes overlap the second electrodes to form an array of capacitors. A controller provides electrical signals to the first and second electrodes to energize and measure the baseline capacitance and repeatedly energize and measure the present capacitance of each capacitor. The controller calculates a ratio function between the present capacitance and the corresponding stored baseline capacitance for each capacitor and provides a touch signal when the ratio function exceeds a predetermined threshold value.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. patent application Ser. No.13/571,704 filed Aug. 10, 2012 entitled Micro-Wire Electrode Pattern, byRonald S. Cok, the disclosure of which is incorporated herein.

FIELD OF THE INVENTION

The present invention relates to control and calibration of capacitorsin capacitive touch screens.

BACKGROUND OF THE INVENTION

Touch screens use a variety of technologies, including resistive,inductive, capacitive, acoustic, piezoelectric, and opticaltechnologies. Such technologies and their application in combinationwith displays to provide interactive control of a processor and softwareprograms are well known in the art. Capacitive touch-screens are of atleast two different types: self-capacitive and mutual-capacitive.Self-capacitive touch-screens employ an array of transparent electrodes,each of which in combination with a touching device (e.g. a finger orconductive stylus) forms a temporary capacitor whose capacitance isdetected. Mutual-capacitive touch-screens can employ an array oftransparent electrode pairs that form capacitors whose capacitance isaffected by a conductive touching device. In either case, each capacitorin the array is tested to detect a touch and the physical location ofthe touch-detecting electrode in the touch-screen corresponds to thelocation of the touch. For example, U.S. Pat. No. 7,663,607 discloses amultipoint touch-screen having a transparent capacitive sensing mediumconfigured to detect multiple touches or near touches that occur at thesame time and at distinct locations in the plane of the touch panel andto produce distinct signals representative of the location of thetouches on the plane of the touch panel for each of the multipletouches. The disclosure teaches both self- and mutual-capacitivetouch-screens.

Referring to FIG. 10, a prior-art display and touch-screen system 100includes a display 110 with a corresponding touch screen 120 mountedwith display 110 so that information displayed on display 110 is viewedthrough touch screen 120. Graphic elements displayed on display 110 areselected, indicated, or manipulated by touching a corresponding locationon touch screen 120. Touch screen 120 includes a first transparentsubstrate 122 with first transparent electrodes 130 formed in the xdimension on the first transparent substrate 122 and a secondtransparent substrate 126 with second transparent electrodes 132 formedin the y dimension facing the x-dimension first transparent electrodes130 on the second transparent substrate 126. A transparent dielectriclayer 124 is located between first and second transparent substrates122, 126 and first and second transparent electrodes 130, 132. Referringalso to the plan view of FIG. 11, in this example first pad areas 128 infirst transparent electrodes 130 are located adjacent to second padareas 129 in second transparent electrodes 132. (The first and secondpad areas 128, 129 are separated into different parallel planes bytransparent dielectric layer 124.) The first and second transparentelectrodes 130, 132 have a variable width and extend in orthogonaldirections (for example as shown in U.S. Patent Publication Nos.2011/0289771 and 2011/0099805). When a voltage is applied across firstand second transparent electrodes 130, 132, electric fields are formedbetween first pad areas 128 of x-dimension first transparent electrodes130 and second pad areas 129 of y-dimension second transparentelectrodes 132.

A display controller 142 (FIG. 10) connected through electrical bussconnections 136 controls display 110 in cooperation with a touch-screencontroller 140. Touch-screen controller 140 is connected throughelectrical buss connections 136 and wires 134 and controls touch screen120. Touch-screen controller 140 detects touches on the touch screen 120by sequentially electrically energizing and testing x-dimension firstand y-dimension second transparent electrodes 130, 132.

Referring to FIG. 12, in another prior-art embodiment, rectangular firstand second transparent electrodes 130, 132 are arranged orthogonally onfirst and second transparent substrates 122, 126 with interveningtransparent dielectric layer 124, forming touch screen 120 which, incombination with the display 110 forms touch-screen and display system100. First and second pad areas 128, 129 are formed where first andsecond transparent electrodes 130, 132 overlap. Touch screen 120 anddisplay 110 are controlled by touch screen and display controllers 140,142, respectively, through electrical buss connections 136 and wires134.

Since touch-screens are largely transparent, any electrically conductivematerials located in the transparent portion of the touch-screen eitheremploy transparent conductive materials or employ conductive elementsthat are too small to be readily resolved by the eye of a touch-screenuser. Transparent conductive metal oxides are well known in the displayand touch-screen industries and have a number of disadvantages,including limited transparency and conductivity and a tendency to crackunder mechanical or environmental stress. Typical prior-art conductiveelectrode materials include conductive metal oxides such as indium tinoxide (ITO) or very thin layers of metal, for example silver or aluminumor metal alloys including silver or aluminum. These materials arecoated, for example, by sputtering or vapor deposition, and arepatterned on display or touch-screen substrates, such as glass. However,the current-carrying capacity of such electrodes is limited, therebylimiting the amount of power that is supplied to the pixel elements.Moreover, the substrate materials are limited by the electrode materialdeposition process (e.g. sputtering). Thicker layers of metal oxides ormetals increase conductivity but reduce the transparency of theelectrodes.

Touch-screens, including very fine patterns of conductive elements, suchas metal wires or conductive traces are known. For example, U.S. PatentPublication No. 2011/0007011 teaches a capacitive touch screen with amesh electrode, as does U.S. Patent Publication No. 2010/0026664.Referring to FIG. 13, a prior-art x- or y-dimension first or secondvariable-width transparent electrode 130, 132 includes a micro-pattern156 of micro-wires 150 arranged in a rectangular grid. Micro-wires 150are multiple, very thin metal conductive traces or wires formed on thefirst and second transparent substrates 122, 126 (not shown in FIG. 13)to form the x- or y-dimension first or second transparent electrodes130, 132. Micro-wires 150 are so narrow that they are not readilyvisible to a human observer, for example 1 to 10 microns wide.Micro-wires 150 are typically opaque and spaced apart, for example by 50to 500 microns, so that first or second transparent electrodes 130, 132appear to be transparent and micro-wires 150 are not distinguished by anobserver.

U.S. Patent Application Publication No. 2011/0291966 discloses an arrayof diamond-shaped micro-wire structures. In this disclosure, a firstelectrode includes a plurality of first conductor lines inclined at apredetermined angle in clockwise and counterclockwise directions withrespect to a first direction and provided at a predetermined interval toform a grid-shaped pattern. A second electrode includes a plurality ofsecond conductor lines, inclined at the predetermined angle in clockwiseand counterclockwise directions with respect to a second direction, thesecond direction perpendicular to the first direction and provided atthe predetermined interval to form a grid-shaped pattern. Thisarrangement is used to inhibit Moiré patterns. The electrodes are usedin a touch screen device. Referring to FIG. 14, this prior-art designincludes micro-wires 150 arranged in a micro-pattern 156 withmicro-wires 150 oriented at an angle to the direction of horizontalfirst transparent electrodes 130 and vertical second transparentelectrodes 132.

Manufacturing techniques for capacitive touch screens having eithertransparent conductive oxide electrodes or electrodes with fine patternsof conductive metal wires are known. These techniques inevitably have amanufacturing variability that causes a performance variation.Furthermore, when in use, the performance of capacitive touch screenscan vary due to use conditions or wear. For example, transparentconductive oxides are known to crack under mechanical stress, whichreduces the conductivity of the materials.

A variety of calibration and control techniques for capacitive touchscreens are taught in the prior art. U.S. Patent Application PublicationNo. 2011/0248955 discloses a touch detection method and circuit forcapacitive touch panels. The touch detection method for capacitive touchpanels includes scanning the rows and columns of the capacitive matrixof a touch panel respectively, wherein during the scanning of the rowsor columns of the capacitive matrix of the touch panel, two rows orcolumns are synchronously scanned at the same time to obtain thecapacitance differential value between the two rows or columns, or onerow or column is scanned at the same time to obtain the capacitancedifferential value between the row or column and a referencecapacitance; and then processing the obtained capacitance differentialvalue.

U.S. Patent Application Publication No. 2010/0244859 teaches acapacitance measuring system including analog-digital calibrationcircuitry that subtracts baseline capacitance measurements fromtouch-induced capacitance measurements to produce capacitance changevalues.

U.S. Pat. No. 8,040,142 discloses touch detection techniques forcapacitive touch sense systems that include measuring a capacitancevalue of a capacitance sensor within a capacitance sense interface toproduce a measured capacitance value. The measured capacitance value isanalyzed to determine a baseline capacitance value for the capacitancesensor. The baseline capacitance value is updated based at least in partupon a weighted moving average of the measured capacitance value. Themeasured capacitance value is analyzed to determine whether thecapacitance sensor was activated during a startup phase and to adjustthe baseline capacitance value in response to determining that thecapacitance sensor was activated during the startup phase.

U.S. Patent Application Publication No. 2012/0043976 teaches a techniquefor recognizing and rejecting false activation events related to acapacitance sense interface includes measuring a capacitance value of acapacitance sense element. The measured capacitance value is analyzed todetermine a baseline capacitance value for the capacitance sensor. Thecapacitance sense interface monitors a rate of change of the measuredcapacitance values and rejects an activation of the capacitance senseelement as a non-touch event when the rate of change of the measuredcapacitance values have a magnitude greater than a threshold value,indicative of a maximum rate of change of a touch event.

Baseline capacitance measurements are useful for initial calibration butare sensitive to problems of drift in the measured baseline values.Absolute difference values can be misleading in the presence of changesin capacitors, for example through wear. Although rate-of-changemeasurements are useful to reject false activation, they do not addressproblems with signal-to-noise ratio in performance variability due tomanufacturing variability or performance changes due to wear. There is aneed, therefore, for improved measurement methods for detecting toucheswith a capacitive touch screens.

SUMMARY OF THE INVENTION

In accordance with the present invention, a touch-screen devicecomprises:

a transparent dielectric layer having a first side and a second sideopposite and substantially parallel to the first side;

a plurality of first electrodes extending in a first length directionlocated over the first side,

a plurality of second electrodes having a second length directiondifferent from the first length direction located under the second sideso that the first electrodes overlap the second electrodes to form anarray of capacitors;

a controller having a memory and circuits that provide electricalsignals to the first and second electrodes, the circuits performing thefollowing functions:

-   -   energizing each capacitor, measuring the baseline capacitance of        each capacitor, and storing the baseline capacitance of each        capacitor in the memory; and    -   repeatedly energizing each capacitor and measuring the present        capacitance of each capacitor; and

the controller calculating a ratio function between the presentcapacitance and the corresponding stored baseline capacitance for eachcapacitor and providing a touch signal when the ratio function exceeds apredetermined threshold value.

The present invention provides a device and method for improving touchdetection for capacitive touch screen in the presence of manufacturingvariability and performance changes due to use.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent when taken in conjunction with the followingdescription and drawings wherein identical reference numerals have beenused to designate identical features that are common to the figures, andwherein:

FIG. 1 is a perspective illustrating an embodiment of the presentinvention;

FIGS. 2-6 are flow diagrams illustrating various embodiments of thepresent invention;

FIG. 7 is a perspective illustrating electrodes in an embodiment of thepresent invention;

FIG. 8 is a plan view illustrating electrodes in an embodiment of thepresent invention;

FIGS. 9A and 9B are cross sections of embodiments of the presentinvention;

FIG. 10 is an exploded perspective illustrating a prior-art mutualcapacitive touch screen having adjacent pad areas in conjunction with adisplay and controllers;

FIG. 11 is a schematic illustrating prior-art pad areas in a capacitivetouch screen;

FIG. 12 is an exploded perspective illustrating a prior-art mutualcapacitive touch screen having overlapping pad areas in conjunction witha display and controllers;

FIG. 13 is a schematic illustrating prior-art micro-wires in anapparently transparent electrode; and

FIG. 14 is a schematic illustrating prior-art micro-wires arranged intwo arrays of orthogonal transparent electrodes.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, in an embodiment of the present invention, atouch-screen device 5 includes a transparent dielectric layer 10 havinga first side 11 and a second side 12 opposite and substantially parallelto the first side 11. A plurality of first electrodes 20 extending in afirst length direction 22 is located over first side 11. A plurality ofsecond electrodes 30 having a second length direction 32 different fromfirst length direction 22 is located under second side 12 so that firstelectrodes 20 overlap second electrodes 30 to form an array ofcapacitors 60. First electrodes 20 are orthogonal to second electrode 30and first and second electrodes 20, 30 can be transparent, or apparentlytransparent.

Four capacitors 60 are indicated in FIG. 1 with dashed lines projectingfrom first electrode 20 to second electrode 30 in the areas of overlapbetween first and second electrodes 20, 30. In FIG. 1, two firstelectrodes 20 are formed in the vertical first length direction 22 overtransparent dielectric layer 10 and two second electrodes 30 are formedin the horizontal second length direction 32 under transparentdielectric layer 10. The overlap of the first and second electrodes 20,30 therefore forms a two-by-two array of capacitors 60. First electrode20 located over transparent dielectric layer 10 is shown with solidlines while second electrode 30 located under transparent dielectriclayer 10 is shown with dashed lines, as are capacitors 60.

A controller 40 having a memory 44 and circuits 42 provides electricalsignals to first and second electrodes 20, 30. The electrical signalscan drive first and second electrodes 20, 30 and also respond to firstand second electrodes 20, 30 through wires 134. Circuits 42 energizeeach capacitor 60 and measure the baseline capacitance of each capacitor60 through first and second electrodes 20, 30. The measured baselinecapacitance of each capacitor 60 is stored in memory 44. Circuits 42repeatedly energize each capacitor 60 and measure the presentcapacitance of each capacitor 60 through first and second electrodes 20,30. Controller 40 calculates a ratio function between the presentcapacitance and the corresponding stored baseline capacitance for eachcapacitor 60 and provides a touch signal when the ratio function exceedsa predetermined threshold value. The baseline capacitance is measuredthe same way as is the present capacitance except that the baselinecapacitance is measured as a calibration step for touch-screen device 5when no touches are expected.

The ratio function is a mathematical operation performed upon a ratio ofthe baseline capacitance and the present capacitance, for example aratio derived by dividing one by the other. In embodiments, either thebaseline capacitance is divided by the present capacitance or thepresent capacitance is divided by the baseline capacitance. The ratiofunction can include other operations, for example adding or subtractingconstants or employing other multipliers or dividers, or other geometricor arithmetic functional transforms including inversion. As describedherein, the ratio function is compared to a threshold value and a touchdetected if the ratio function exceeds the threshold value. However, aswill be appreciated by those skilled in mathematics, the ratio functioncan be inverted so that an equivalent operation is performed bydetecting if the ratio function is less than a threshold value. Thepresent invention includes touch determinations both when the ratiofunction exceeds a threshold value and when the ratio function is lessthan a threshold value. The description of less than or greater than athreshold value is arbitrary and used for convenience and a less thancomparison can be exchanged with a greater than comparison withoutlimiting the scope of the present invention. The term “ratio function”as used herein can also mean the value of the ratio function whenapplied to input parameters including a ratio of the baselinecapacitance and present capacitance.

Furthermore, as used herein, a touch can be indicated with a ratiofunction that is greater than the predetermined threshold value or thatis greater than or equal to the predetermined threshold value. Thephrase “greater than” is used for concision and the invention includescomparisons that are greater than or greater than or equal to. Likewise,as discussed below, the phrase “less than” is used for concision and theinvention includes comparisons that are less than or less than or equalto.

Transparent dielectric layers 10 with opposing parallel first and secondsides 11, 12 can include substrates made of, for example, glass orpolymers and are known in the art. Such transparent dielectric layers 10can be, for example, 10 microns-1 mm thick, or more, for example 1-5 mmthick; the present invention is not limited to any particular thickness.First and second electrodes 20, 30 are, for example, formed on opposingsides of transparent dielectric layer 10 using photolithographic methodsknown in the art, for example sputtering, patterned coating, orunpatterned coating followed by coating with photosensitive materialthat is subsequently patterned with light, patterned removal, andetching.

First and second electrodes 20, 30 can be formed on transparentdielectric layer 10, on layers formed on transparent dielectric layer10, or on other substrates (not shown) arranged to locate firstelectrode 20 over first side 11 of transparent dielectric layer 10 andsecond electrode 30 under second side 12 of transparent dielectric layer10. First and second electrodes 20, 30 can include, for example,materials such as transparent conductive oxides, thin metal layers, orpatterned metal micro-wires. Materials, deposition, and patterningmethods for forming electrodes on dielectric substrates are known in theart and can be employed in concert with the present invention.

First length direction 22 of first electrode 20 or second lengthdirection 32 of second electrode 30 is typically the direction of thegreatest spatial extent of corresponding first or second electrode 20,30 over, on, or under a side of transparent dielectric layer 10 (e.g.first side 11 or second side 12). Electrodes formed on or oversubstrates are typically rectangular in shape, or formed of rectangularelements, with a length and a width, and the length is much greater thanthe width. See, for example, the prior-art illustrations of FIG. 12. Inany case, first or second length direction 22, 32 can be selected to bea direction of desired greatest extent of first or second electrode 20,30 respectively. Electrodes are generally used to conduct electricityfrom a first point on a substrate to a second point and the direction ofthe electrode from the first point to the second point can be the lengthdirection.

Controller 40 can be a digital or analog controller 40, for example atouch-screen controller, can include a processor, logic circuits,programmable logic arrays, one or more integrated or discrete circuitson one or more printed circuit boards, or other computational andcontrol elements providing circuits 42 and a memory 44 and can includesoftware programs or firmware. The electrical signals are, for example,electronic analog or digital signals. Signals can be measured as analogvalues and converted to digital values. Signals can be, for example,current values or voltage values. Such control, storage, computational,and signaling devices, circuits, and memories are known in the art andcan be employed with the present invention.

Capacitors 60 are formed where first and second electrodes 20, 30overlap and store charge when energized, for example by providing avoltage differential across first and second electrodes 20, 30. Thecharge for each capacitor 60 can be measured using circuits 42 incontroller 40 and the measured capacitance value stored in memory 44. Byrepeatedly providing a voltage differential across first and secondelectrodes 20, 30 and measuring it, the capacitance of capacitors 60 arerepeatedly measured over time. Time-base circuits, such as clocks, arewell known in the computing arts and can be employed here. For example,a clock signal, as well as other control signals, is supplied tocontroller 40.

The initial capacitance measurement of each capacitor 60 is taken, forexample when touch-screen device 5 is manufactured or the first timetouch-screen device 5 is powered up in the absence of any externalconductive element, for example a finger or conductive stylus. Thisinitial capacitance measurement provides a baseline capacitancemeasurement against which subsequent capacitance measurements are madeto identify differences in capacitance that can indicate a touch. Suchcontrol methods and circuits are well known in the display and touchscreen industries and can be applied here. The subsequent capacitancemeasurements are identified as present capacitance measurements as theyare taken in the present, i.e. in real-time when touch-screen device 5is in use. The present capacitance measurements are taken repeatedly andcan be taken periodically as controlled by a clock signal. Touch-screendevice 5 can, when no changes in capacitance are detected (i.e. notouches are detected) over a length of time, power down and ceaseoperation until some other event occurs that causes controller 40 toagain measure the capacitor 60 capacitance.

Referring to FIG. 2, capacitors 60 are energized 200 by providing powerto first and second electrodes 20, 30 and the initial baselinecapacitance is measured 205 and stored 210 by controller 40, circuits 42and memory 44 for each capacitor 60. A test is performed 215 to ensurethat the capacitance of capacitors 60 is measured. If not, thecapacitance of remaining capacitors 60 is measured. If so, capacitors 60are energized 200 again and the present capacitance measured 220 foreach capacitor 60. Controller 40 calculates 225 a ratio functionincorporating a ratio of the baseline and present capacitance. Aseparate ratio function is calculated for each capacitor 60. Thebaseline capacitance for each capacitor 60 is found by accessing memory44 and retrieving the baseline capacitance value, for example byproviding an address for each capacitor 60 and using the address tostore the measured baseline capacitance corresponding to the addressedcapacitor 60. Present capacitance values for each capacitor 60 can alsobe stored. Methods and circuits for storing and accessing data and usinglookup tables are well known in the digital computing arts.

The calculated ratio function for each capacitor 60 is tested 230 bycomparing the calculated ratio function to a predetermined thresholdvalue. If the predetermined threshold value is exceeded, a touch isdetected 235 and a touch signal provided 240 by controller 40, forexample to a display controller (e.g. display controller 142 in FIG. 10)or computer. The process is then repeated 245 for a next capacitor 60.The process for repeatedly measuring capacitance for a capacitivetouch-screen (e.g. touch-screen device 5) is well known and processesand circuits to repeatedly test and measure the capacitance of arrays ofcapacitors 60 are well known.

Steps 200-215 of FIG. 2 can be considered to make up a calibration step300 while steps 220-245 make up an operation step 305. Referring furtherto FIG. 3, calibration step 300 can be repeated after one or moreoperation steps 305. For example, a clock signal can periodicallyinterrupt operational step 305 to test 310 if the baseline capacitancemeasurements should be updated. If not, operational steps 305recommence. If so, calibration process 300 (FIG. 2) is repeated.Calibration process 300 can be repeated for a variety of reasons, forexample periodically, to avoid drift in the capacitance measurements, inresponse to the presence of environmental or use changes, or in responseto operation of the device elements such as first or second electrodes20, 30 due to use. Thus, circuits 42 repeatedly energize 200 eachcapacitor 60, measure 205 an updated capacitance of each capacitor 60,and store 210 the updated baseline capacitance in the memory 44. Theupdated baseline capacitance values are then used to calculate the ratiofunction used in subsequent touch determinations 235. A history ofbaseline values can be maintained in the memory 44.

In actual use, the measured present capacitance values can be noisy andfalse positive or false negative touch determinations made. To avoidsuch false signals, referring to FIG. 4 in another embodiment, the ratiofunction indicating a touch can be limited to a range such that theratio function can be greater than the predetermined threshold value butalso less than a second predetermined threshold value that is greaterthan the predetermined value. Thus, the process for determining a touchincludes calculating the ratio function (step 225 in FIG. 2), testing230 the ratio function against the predetermined threshold value (e.g.by a comparison), and then testing 231 the ratio function against asecond predetermined threshold value (e.g. by a comparison). Only ifboth tests are positive is a touch detected 235 and a touch signalprovided 240 by the controller 40. Once a capacitor 60 is measured andits capacitance measured, a ratio function calculated and touchdetermined, the next capacitor 60 can be tested 245. By requiring twocomparisons within a threshold range to determine a touch, voltagespikes or false positives from other anomalous signals can be avoided.

Referring to FIG. 5, in another embodiment of the present invention, twosubsequent capacitor 60 measurements are tested twice sequentially. Afirst ratio function is tested 230 and if the result is negative, atouch value is marked 243 as “touch off” (e.g. a Boolean data value in acomputer program is assigned to a negative or zero value). If the resultis positive, a touch is detected 235 but the touch value is tested 236to determine if a prior touch was detected. If the touch value ispositive, a prior touch is assumed, the touch signal is provided 240 andthe next capacitor 60 tested 245. If the touch value is negative, aprior touch is not assumed, the touch value is marked 242 as “touch on”(e.g. a Boolean data value in a computer program is assigned to apositive or one value) and the next capacitor 60 is tested 245 but notouch signal is provided (i.e. step 240 is not performed). Such analgorithm is performed by a processor executing a software program orfirmware, or by a logic state machine. Such devices capable ofperforming the algorithm of FIG. 5 are known in the art.

By requiring that a touch be detected twice sequentially, spurious,intermittent or too-short touches are ignored. A delay can beimplemented within the process to require that a certain length of time,for example one millisecond, elapse before a touch signal is provided.Alternatively or in addition, more than two sequential touches aredetected before a touch signal is provided. This can be accomplished,for example, by using a multi-valued touch value, incrementing themulti-valued touch value with each subsequent touch (corresponding tostep 242), and providing the touch signal when the multi-valued touchvalue reaches a desired number of repetitions, e.g. five.

In another embodiment of the present invention, referring to FIG. 6, adifferent third predetermined threshold value less than thepredetermined threshold value is used to indicate that a touch is nolonger present. This provides hysteresis in the control system andavoids frequent switching between states when a ratio function is closeto the predetermined threshold. As shown in FIG. 6, if the ratiofunction exceeds the predetermined threshold (230), a touch value ismarked 242 on, tested 236, and a touch signal provided 240. If the ratiofunction does not exceed the predetermined threshold (230), the ratiofunction is tested 232 against a third predetermined threshold value. Ifthe ratio function is less than the third predetermined threshold value,the touch value is marked off 243 and no touch signal is provided. Ifthe ratio function is not less than the third predetermined thresholdvalue, the touch value is tested 236, and, if positive, indicating thata touch was previously detected, a touch signal is provided. Ifnegative, no touch was previously detected, and a touch signal is notprovided. The next capacitor 60 is then tested 245. Thus, according toan embodiment of the present invention, controller 40 provides a secondtouch signal when the ratio function is less than a third predeterminedthreshold value after a touch signal is first provided, the thirdpredetermined value is less than the predetermined threshold value.

The methods and algorithms described above can be combined, as will beappreciated by those skilled in the controller arts. For example,sequential touch detections are required separated over a desired timespan to provide a touch signal and hysteresis is provided to indicatetouch signal cessation.

In a further embodiment of the present invention, transparent dielectriclayer 10 is flexible and at least one capacitor 60 changes capacitancewhen transparent dielectric layer 10 is flexed. In an embodiment, thechange in capacitance is permanent. In an alternative embodiment, firstand second electrodes 20, 30 are electrically conductive, transparentdielectric layer 10 is flexible, and at least one of first or secondelectrodes 20, 30 changes its electrical conductivity when transparentdielectric layer 10 is flexed. Such a change in conductivity can lead toperformance changes in the rate at which capacitors 60 are charged ordischarged or the capacitance of capacitors 60. In an embodiment, thechange in electrical conductivity is permanent.

The baseline capacitance values for affected capacitors 60 can alsochange when the capacitance of capacitors 60 or the conductivity offirst or second electrodes 20, 30 changes. Hence, prior-art methods thatrely on the absolute capacitance value of capacitors 60 can be lessreliable than the present invention when touch-screen device 5 is used.

As shown in FIGS. 7 and 8 (and also in FIG. 1), in another embodiment,first and second electrodes 20, 30 extending in first and second lengthdirections 22, 32 respectively, each include a plurality of electricallyconnected micro-wires 50. Micro-wires 50 are spatially separated toprovide apparently transparent first and second electrodes 20, 30. InFIGS. 1, 7, and 8 micro-wires 50 of first electrode 20 are shown withsolid lines while micro-wires 50 of second electrode 30 are shown withdashed lines. Micro-wires 50 are illustrated in a rectangular meshconfiguration in FIG. 1 while in FIGS. 7 and 8 straight micro-wires 50extend in the corresponding electrode length direction (e.g. 22, 32) andangled micro-wires 50 electrically connect the straight micro-wires 50so that micro-wires 50 of first electrode 20 are parallel to micro-wires50 of second electrode 30. Parallel micro-wires 50 in first and secondelectrodes 20, can increase the capacitance of capacitor 60 formed bythe overlap of first electrode 20 with second electrode 30 and improvethe signal-to-noise ratio of the measured capacitance.

In another embodiment, transparent dielectric layer 10 is flexible,micro-wires 50 are electrically conductive, and the electricalconductivity of at least one micro-wire 50 changes when transparentdielectric layer 10 is flexed. In a further embodiment, the change inelectrical conductivity is permanent. For example, micro-wires 50 cancrack and form an electrical open. Since multiple electrically connectedmicro-wires 50 are present in first or second electrode 20, 30, such achange in a single micro-wire 50 need not cause first or secondelectrode 20, 30 to fail.

Referring to FIGS. 9A and 9B, in alternative embodiments, touch-screendevice 5 includes a display 70 having a cover or substrate 72. First orsecond electrodes 20, 30 are formed on cover or substrate 72 or onlayers formed on cover or substrate 72. In the embodiment of FIG. 9A,transparent dielectric layer 10 is cover or substrate 72 and first andsecond electrodes 20, 30 are located on opposing sides of cover orsubstrate 72. In the embodiment of FIG. 9B, transparent dielectric layer10 is separate from cover or substrate 72 and second electrode 30 islocated over cover or substrate 72 outside the display 70 and betweencover or substrate 72 and transparent dielectric layer 10. A protectivecover 80 is provided over first electrodes 20 in both alternativeembodiments.

Transparent dielectric layer 10 of the present invention can be asubstrate and can include any dielectric material capable of providing asupporting surface on which first or second electrodes 20, 30 ormicro-wires 50 can be formed and patterned. Substrates made of glass orplastics can be used and are known in the art together with methods forproviding suitable surfaces. Transparent dielectric layer 10 issubstantially transparent, for example having a transparency of greaterthan 90%, 80%, 70%, or 50% in the visible range of electromagneticradiation.

First or second electrodes 20, 30 can be formed directly on transparentdielectric layer 10 or over transparent dielectric layer 10 on layersformed on transparent dielectric layer 10. The words “on”, “over”, orthe phrase “on or over” indicate that micro-wires 50 of first or secondelectrodes 20, 30 of the present invention can be formed directly ontransparent dielectric layer 10, on layers formed on transparentdielectric layer 10, or on other layers or on another substrate locatedso that first electrodes 20 are over transparent dielectric layer 10.Likewise, second electrodes 30 can be formed under or beneathtransparent dielectric layer 10 or on another substrate located so thatsecond electrodes 30 are under transparent dielectric layer 10. Thewords “on”, “under”, “beneath” or the phrase “on or under” indicate thatmicro-wires 50 of first or second electrodes 20, of the presentinvention can be formed directly on transparent dielectric layer 10, onlayers formed on transparent dielectric layer 10, or on other layers oranother substrate located so that first electrodes 20 are overtransparent dielectric layer 10 and second electrodes 30 are undertransparent dielectric layer 10. “Over” or “under”, as used in thepresent disclosure, are simply relative terms for layers located on oradjacent to opposing surfaces of transparent dielectric layer 10. Byflipping transparent dielectric layer 10 and related structures orsubstrates over as a unit, layers that are over transparent dielectriclayer 10 become under transparent dielectric layer 10 and layers thatare under transparent dielectric layer 10 become over transparentdielectric layer 10.

First or second electrodes 20, 30 can be formed on transparentsubstrates separate from transparent dielectric layer 10. Alternatively,first or second electrodes 20, 30 can be formed on transparentdielectric layer 10, or some combination of transparent dielectric layer10 and other transparent substrates. Micro-wires 50 for each of firstand second transparent electrodes 20, 30 can be formed on opposing sidesof the same transparent substrate (e.g. as shown in FIG. 1) or on facingsides of separate transparent substrates or some combination of thosearrangements.

The length direction of first or second electrode 20, 30 (e.g. first andsecond length direction 22, 32, respectively) is typically the directionof the greatest spatial extent of the corresponding first or secondelectrode 20, 30 over transparent dielectric layer 10 over or underwhich first or second electrodes 20, are located. Electrodes located on,over, or under substrates are typically rectangular in shape, or formedof rectangular elements, with a length and a width, where the length ismuch greater than the width. See, for example, the prior-artillustrations of FIG. 12. Electrodes are generally used to conductelectricity from a first point on a substrate to a second point and thedirection of the electrode from the first point to the second point canbe the length direction of the electrode.

Touch-screen device 5 of the present invention can be used in atouch-screen and display system 100, such as illustrated in theperspective of FIG. 10 or 12. Wires 134, buss connections 136, anddisplay controller 142 of FIG. 10 can be used as described withreference to FIG. 10. In response to a voltage differential providedbetween electrodes on either side of transparent dielectric layer 10, anelectrical field is formed and a capacitance produced. Touch-screencontroller 40 (FIG. 1) sequentially energizes first and secondelectrodes 20, 30 (e.g. with a voltage differential) and senses acapacitance. The capacitance of overlapping electrode areas (capacitors60) is changed in the presence of a conductive element, such as a fingeror conductive stylus. The change in capacitance is detected andindicates a touch. By providing a controller 40 of the presentinvention, more robust touch sensing can be provided, especially in thepresence of environmental variability and particular due to device wear,for example from use.

In an example and non-limiting embodiment of the present invention, eachmicro-wire 50 is 5 microns wide and separated from neighboringmicro-wires 50 in an electrode by a distance of 50 microns, so that thetransparent electrode (e.g. first or second electrode 20, 30) formed bymicro-wires 50 is 90% transparent. As used herein, transparent refers toelements that transmit at least 50% of incident visible light,preferably 80%, or at least 90%. Micro-wires 50 can be arranged in amicro-pattern 156 that is unrelated to the pattern of first or secondelectrodes 20, 30. Micro-patterns 156 other than those illustrated inthe Figures can be used in other embodiments and the present inventionis not limited by the pattern of first or second electrodes 20, 30 ormicro-wires 50.

Micro-wires 50 can be metal, for example silver, gold, aluminum, nickel,tungsten, titanium, tin, or copper or various metal alloys including,for example silver, gold, aluminum, nickel, tungsten, titanium, tin, orcopper. Micro-wires 50 are, for example formed in a thin metal layercomposed of highly conductive metals. Other conductive metals ormaterials can be used. Micro-wires 50 can be, but need not be, opaque.Micro-wires 50 can be formed by patterned deposition of conductivematerials or of patterned precursor materials that are subsequentlyprocessed, if necessary, to form a conductive material. Suitable methodsand materials are known in the art, for example, inkjet deposition orscreen printing with conductive inks. Alternatively, micro-wires 50 areformed by providing a blanket deposition of a conductive or precursormaterial and patterning and curing, if necessary, the deposited materialto form a micro-pattern 156 of micro-wires 50. Photo-lithographic andphotographic methods are known to perform such processing. The presentinvention is not limited by the micro-wire materials or by methods offorming a pattern of micro-wires 50 on a supporting substrate surface.

Alternatively, micro-wires 50 can include cured or sintered metalparticles such as nickel, tungsten, silver, gold, titanium, or tin oralloys such as nickel, tungsten, silver, gold, titanium, or tin. Othermaterials or methods for forming micro-wires 50 can be employed and areincluded in the present invention.

As used herein, micro-wires 50 in first or second electrodes 20, 30 aremicro-wires 50 formed in a micro-wire layer that forms a conductive meshof electrically connected micro-wires 50. If a transparent substrate onwhich micro-wires 50 are formed is planar, for example, a rigid planarsubstrate such as a glass substrate, micro-wires 50 in a micro-wirelayer are formed in, or on, a common plane as a conductive, electricallyconnected mesh. If a transparent substrate is flexible and curved, forexample a plastic substrate, micro-wires 50 in a micro-wire layer are aconductive, electrically connected mesh that is a common distance from asurface of the flexible, transparent substrate.

In embodiments of the present invention, micro-wires 50 are made bydepositing an unpatterned layer of material and then differentiallyexposing the layer to form the different micro-wire 50 micro-patterns156. For example, a layer of curable precursor material is coated over asubstrate and pattern-wise exposed. The material is exposed in a commonstep or in different steps. A variety of processing methods can be used,for example photo-lithographic or silver halide methods. The materialscan be differentially pattern-wise exposed and then processed.

A variety of materials can be employed to form patterned micro-wires 50including resins that can be cured by cross-linkingwave-length-sensitive polymeric binders and silver halide materials thatare exposed to light. Processing can include both washing out residualuncured materials and curing or exposure steps.

In an embodiment, a precursor layer includes conductive ink, conductiveparticles, or metal ink. The exposed portions of the precursor layer arecured to form micro-wires 50 (for example by exposure to patterned laserlight to cross-link a curable resin) and the uncured portions removed.Alternatively, unexposed portions of the first and second micro-wirelayers are cured to form micro-wires 50 and the cured portions removed.

In another embodiment of the present invention, the precursor layers aresilver salt layers. The silver salt can be any material that is capableof providing a latent image (that is, a germ or nucleus of metal in eachexposed grain of metal salt) according to a desired pattern uponphoto-exposure. The latent image can then be developed into a metalimage. For example, the silver salt can be a photosensitive silver saltsuch as a silver halide or mixture of silver halides. The silver halidecan be, for example, silver chloride, silver bromide, silverchlorobromide, or silver bromoiodide.

According to some embodiments, the useful silver salt is a silver halide(AgX) that is sensitized to any suitable wavelength of exposingradiation. Organic sensitizing dyes can be used to sensitize the silversalt to visible or IR radiation, but it can be advantageous to sensitizethe silver salt in the UV portion of the electromagnetic spectrumwithout using sensitizing dyes.

Processing of AgX materials to form conductive traces typically involvesat least developing exposed AgX and fixing (removing) unexposed AgX.Other steps can be employed to enhance conductivity, such as thermaltreatments, electroless plating, physical development and variousconductivity enhancing baths, e.g., as described in U.S. Pat. No.3,223,525.

To achieve transparency, the total area occupied by micro-wires 50 canbe less than 15% of the area of first or second electrode 20, 30.

In an embodiment, the first and second precursor material layers caneach include a metallic particulate material or a metallic precursormaterial, and a photosensitive binder material.

In any of these cases, the precursor material is conductive after it iscured and any needed processing completed. Before patterning or beforecuring, the precursor material is not necessarily electricallyconductive. As used herein, precursor material is material that iselectrically conductive after any final processing is completed and theprecursor material is not necessarily conductive at any other point inthe micro-wire formation process.

Methods and device for forming and providing substrates, coatingsubstrates, patterning coated substrates, or pattern-wise depositingmaterials on a substrate are known in the photo-lithographic arts.Likewise, tools for laying out electrodes, conductive traces, andconnectors are known in the electronics industry as are methods formanufacturing such electronic system elements. Hardware controllers forcontrolling touch screens and displays and software for managing displayand touch screen systems are well known and can be employed with thepresent invention. Tools and methods of the prior art can be usefullyemployed to design, implement, construct, and operate the presentinvention. Methods, tools, and devices for operating capacitive touchscreens can be used with the present invention.

Touch-screen device 5 of the present invention can be usefully employedwith display devices of the prior art. Such devices can include, forexample, OLED displays and lighting, LCD displays, plasma displays,inorganic LED displays and lighting, electrophoretic displays,electrowetting displays, dimming mirrors, smart windows, transparentradio antennae, transparent heaters and other touch screen devices suchas resistive touch screen devices.

The invention has been described in detail with particular reference tocertain embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

PARTS LIST

-   5 touch-screen device-   10 transparent dielectric layer, substrate-   11 first side-   12 second side-   20 first electrode-   22 first length direction-   30 second electrode-   32 second length direction-   40 controller-   42 circuits-   44 memory-   50 micro-wires-   60 capacitor-   70 display-   72 cover or substrate-   80 protective cover-   100 touch-screen and display system-   110 display-   120 touch screen-   122 first transparent substrate-   124 transparent dielectric layer-   126 second transparent substrate-   128 first pad area-   129 second pad area-   130 first transparent electrode-   132 second transparent electrode-   134 wires-   136 buss connections-   140 touch-screen controller-   142 display controller-   150 micro-wire-   156 micro-pattern-   200 energize capacitor step-   205 measure baseline capacitance step-   210 store baseline capacitance step-   215 test capacitors done step-   220 measure present capacitance step-   225 calculate ratio step-   230 test ratio greater than threshold value step-   231 test ratio less than second threshold value step-   232 test ratio less than third threshold value step-   235 touch detected step-   236 test touch value step-   240 provide touch signal step-   241 turn off touch signal step-   242 mark touch on step-   243 mark touch off step-   245 next capacitor step-   300 calibration step-   305 operation step-   310 test update baseline step

1. A touch-screen device, comprising: a transparent dielectric layerhaving a first side and a second side opposite and substantiallyparallel to the first side; a plurality of first electrodes extending ina first length direction located over the first side, a plurality ofsecond electrodes having a second length direction different from thefirst length direction located under the second side so that the firstelectrodes overlap the second electrodes to form an array of capacitors;a controller having a memory and circuits that provide electricalsignals to the first and second electrodes, the circuits performing thefollowing functions: energizing each capacitor, measuring the baselinecapacitance of each capacitor, and storing the baseline capacitance ofeach capacitor in the memory; and repeatedly energizing each capacitorand measuring the present capacitance of each capacitor; and thecontroller calculating a ratio function between the present capacitanceand the corresponding stored baseline capacitance for each capacitor andproviding a touch signal when the ratio function exceeds a predeterminedthreshold value.
 2. The touch-screen device of claim 1, wherein thefirst electrodes are orthogonal to the second electrodes.
 3. Thetouch-screen device of claim 1, wherein the first or second electrodesare formed on the transparent dielectric layer or on layers formed onthe dielectric layer.
 4. The touch-screen device of claim 1, furtherincluding a display having a cover or substrate and wherein the first orsecond electrodes are formed on the cover or substrate or on layersformed on the cover or substrate or wherein the transparent dielectriclayer is the cover or substrate.
 5. The touch-screen device of claim 1,wherein the transparent dielectric layer is flexible and at least onecapacitor changes capacitance when the transparent dielectric layer isflexed.
 6. The touch-screen device of claim 1, wherein the change incapacitance is permanent.
 7. The touch-screen device of claim 1, whereinthe first and second electrodes are electrically conductive, thetransparent dielectric layer is flexible, and at least one of the firstor second electrodes changes its electrical conductivity when thetransparent dielectric layer is flexed.
 8. The touch-screen device ofclaim 7, wherein the change in electrical conductivity is permanent. 9.The touch-screen device of claim 1, wherein the circuits furtherrepeatedly energize each capacitor, measure an updated capacitance ofeach capacitor, and store the updated baseline capacitance in thememory.
 10. The touch-screen device of claim 1, wherein the controllerprovides the touch signal when the ratio function exceeds thepredetermined threshold value two or more times sequentially.
 11. Thetouch-screen device of claim 10, wherein the controller provides thetouch signal when the present capacitance is measured at two differenttimes separated by at least one millisecond.
 12. The touch-screen deviceof claim 1, wherein the controller provides the touch signal when theratio function is less than a second predetermined threshold valuegreater than the predetermined threshold value.
 13. The touch-screendevice of claim 12, wherein the controller provides a second touchsignal when the ratio function is less than a third predeterminedthreshold value after a touch signal is first provided, the thirdpredetermined threshold value being less than the predeterminedthreshold value.
 14. The touch-screen device of claim 13, wherein thecontroller provides the touch signal when the present capacitance ismeasured at two different times separated by at least one millisecond.15. The touch-screen device of claim 11, wherein the controller providesthe touch signal when the present capacitance is measured at twodifferent times separated by at least one millisecond.
 16. Thetouch-screen device of claim 1, wherein the first and second electrodeseach have a plurality of electrically connected micro-wires.
 17. Thetouch-screen device of claim 15, wherein one or more of the micro-wiresof the first electrode are parallel to the micro-wires of the secondelectrode.
 18. The touch-screen device of claim 15, wherein thetransparent dielectric layer is flexible, the micro-wires areelectrically conductive, and the electrical conductivity of at least onemicro-wire changes when the transparent dielectric layer is flexed. 19.The touch-screen device of claim 18, wherein the change in electricalconductivity is permanent.